In the field of equipment for environmental analysis, process analysis, laboratory analysis, and industrial analysis, measuring instruments and measuring systems that display measurement signals measured by various kinds of sensors or that convert the signals into an analog output for transmission are generically called transducers. Generally, such transducers are provided with switches or like operating parts for making settings for the transducer itself or for controlling the sensor.
FIG. 7 shows a prior art transducer. In the figure, the transducer 10 is connected to a sensor 11 and external power supply 12, and the output of the transducer 10 is coupled to a computer 14 via an A/D converter 13, if necessary. The transducer 10 comprises a measuring section 101 for making measurements, an operation section 102 having switches or the like, and a display section 103 for displaying measurement data.
The measuring operation in FIG. 7 will be described step by step. First, the sensor 11 is set ready for the measurement. After that, power is turned on to the transducer 10. Next, the transducer 10 is placed in a setup mode, and various settings, such as the setting of upper and lower set values for the measurement range, the setting of alarm set points, the setting for temperature compensation, and the setting of response speed, are made from the operation section 102 of the transducer 10. When the measurement setup of the transducer 10 is completed, the transducer 10 is placed in a measurement mode to start the measurement. Measurement data is transmitted from the sensor 11 and displayed on the display section 103. Then, the transducer 10 is switched to a transmission mode to transmit the measurement data to the computer 14 for analysis.
In the prior art, analog transmission (DC 4 to 20 mA, etc.) or serial data communication such as RS-232C has been used as a method for transmitting the measurement data from the transducer to the computer.
In the case of analog transmission, the A/D converter 13 for converting the data into a digital signal must be provided as shown by dashed lines, thus requiring the use of an extra device before connection to the computer 14.
In the case of serial communication using RS-232C, the A/D converter is not needed, but few instruments are equipped with RS-232C and, if equipped with RS-232C, such instruments are often expensive; for this reason, in the field of equipment for environmental analysis, process analysis, laboratory analysis, and industrial analysis, measuring systems using RS-232C are not prevalent (reference document 1).
Another method of transmission is one that uses the GPIB (General Purpose Interface Bus) interface. This interface allows a number of devices to be connected in a daisy chain on a single bus. However, equipment that uses this interface system is bulky, its volume being as large as 100 cm3 or more, and requires the use of an independent power supply. GPIB ensures reliable data transmission by using a method called three-wire handshaking. While reliable data transmission can be achieved, GPIB is slow in such cases as when a setup operation and a measurement value read operation are repeated. (Reference document 2)
There is a high-speed version of GPIB, but this is intended for the transmission of large volumes of data (such as waveform data). Further, the cable length of GPIB is specified in the standard, and the expensive cable is usually rugged and bulky.
In the prior art, when processing a plurality of measurement data by computer, a plurality of arrays of sensors 11a to 11e, transducers 10a to 10e, and computers 14a to 14e have been arranged as shown in FIG. 8, and the processing has been performed using a data management device 15. As a result, the overall system becomes large, causing problems in terms of space and cost. (Reference document 3)
Furthermore, it has not been possible to control the transducer 10 from the computer 14, and power has had to be supplied externally.
Reference document 1: Yokogawa Technical Report, Vol. 44, No. 1, 2000, pp. 19-24.
Reference document 2: http://www.ocs-1v.co.jp/LabVIEW/Sub3—5.htm
Reference document 3: http://toyonakakeisou.com/02FA/01Keisoku/01Keisoku.htm